The present invention relates to an engine unit for a vehicle, which includes an oil pump for lubrication and is to be mounted on a scooter-type motorcycle.
In general, an engine unit to be mounted on a vehicle such as a motorcycle and an automobile has a structure in which a crankshaft is rotatably supported in the inside of an engine case (i.e., a crankcase) and an oil pump is bolted so that rotation of the crankshaft is transmitted to the oil pump at a reduced speed through reduction gears, a chain and the like.
Placement of the oil pump in the inside of the engine case however requires a working process to provide a mounting surface exclusively used for the oil pump in the inside of the engine case, leading to difficulty in manufacturing the engine case. In addition, there are required many parts such as bolts for fixing the oil pump, exclusive parts of reduction gear and the like, leading to an increased number of structural parts and resulting in an unavoidable increase in manufacturing cost of the engine unit.
An object of the present invention is therefore to eliminate defects or drawbacks encountered in the prior art mentioned above and to provide an engine unit of a vehicle, which permits not only easy manufacture of the engine case and reduction in number of structural parts to thereby achieve reduction in manufacturing cost of the engine unit, but also improvement in detachability of the oil pump as well as damping effect of a torsion damping device provided on the counter shaft.
The above and other objects can be achieved according to the present invention by providing an engine unit for a vehicle, comprising an engine case in which a crankshaft and a counter shaft are rotatably supported and an oil pump is provided so that rotation of the crankshaft is transmitted to the counter shaft at a reduced speed, wherein the counter shaft is arranged so as to serve as a driving shaft of the oil pump which is arranged coaxial with the counter shaft, the oil pump has a pump case, which is provided with a tubular engaging member concentrically surrounding the counter shaft to extend in an axial direction thereof and with a discharge passage extending so as to be apart from the counter shaft in the axial direction thereof, the tubular engaging member being fitted into a fitting hole for a counter shaft bearing, which is arranged on the engine case side, and the discharge passage having an end portion fitted into an oil supply port formed in the engine case.
In a preferred embodiment of the above aspect, the tubular engaging member has an outer diameter, which is equal to an outer diameter of the counter shaft bearing, which is fitted into the fitting hole.
The engine case is divided at a position of the fitting hole for the counter shaft bearing and a C-shaped ring is fitted between an outer peripheral surface of the tubular engaging member and an inner peripheral surface of the fitting hole for the counter shaft bearing so as to restrict movement of the oil pump in the axial direction.
The pump case is divided into one and another case bodies which are secured together by means of a plurality of bolts so as to provide a liquid tight structure, and the tubular engagement portion is integrally formed with one of the case bodies so as to coaxially surround the periphery of the counter shaft to extend rightward in the axial direction and the other one of the case bodies has a suction port and a discharge port, which surround the respective half peripheral portions of the counter shaft.
The counter shaft is provided with a shock absorbing mechanism for absorbing shock due to variation in torque, and the shock absorbing mechanism has an output side end to which the oil pump is provided.
The oil pump is a trochoid pump.
The vehicle is preferably of a scooter-type motorcycle.
The present invention may be referred to as a modified aspect of an engine unit for a vehicle, which comprises:
an engine case in which a crankshaft and a counter shaft are rotatably supported so that rotation of the crankshaft is transmitted to the counter shaft at a reduced speed; and
an oil pump arranged coaxially with the counter shaft serving as a driving shaft of the oil pump,
the oil pump having a pump case, which is provided with a tubular engaging member concentrically surrounding the counter shaft so as to extend in an axial direction thereof and a discharge passage extending so as to be apart from the counter shaft in the axial direction thereof, the tubular engaging member being fitted into a fitting hole formed to a counter shaft bearing supporting the counter shaft and being arranged on the engine case side, and the discharge passage having an end portion fitted into an oil supply port formed to the engine case.
According to such a structure, the tubular engaging member of the pump case is fitted into the fitting hole for the counter shaft bearing, which is originally formed on the engine case by a working process, so that the oil pump is held in the inside of the engine case. As a result, it become unnecessary to form an additional mounting surface for the oil pump on the engine case by a working process and prepare any bolts for fixing the oil pump and the like. A system in which the counter shaft directly drives the oil pump, makes the reduction gears and the like unnecessary.
Furthermore, it is possible to form the fitting holes for the counter shaft bearings as a hole having a constant inside diameter, leading to an easier working process of the engine case.
Moreover, the single C-shaped ring can surely restrict movement of the oil pump in the axial direction, resulting in a simplified structure. In addition, by putting the engine case in a separate state in the position of the fitting hole for the counter shaft bearing, it becomes possible to detach the oil pump from the engine case, thus improving detachability of the oil pump.
Still furthermore, it becomes possible to improve a damping effect of the shock absorbing mechanism through rotational resistance of the oil pump.
The nature and further characteristic features of the present invention will be made more clear from the description made with reference to the accompanying drawings.